A great place for backpacking in Hawaii is Volcano National Park and specifically the Puna Trail. If you look wilderness snorkeling I suggest looking at Halape Iki and Keauhou Landing. Keauhou Landing has the best coral on all the island and probably in the Islands.
While staying in Kona, we opted to travel to the Volcano National Park. We had our own vehicle and traveled thru the town of Hilo in order to get to the National Park. The park was amazing. Sadly, it rained the majority of the time. It is apparently very common for rain to occur. There was plenty to see and much to read. The fact that you could see steam rising thru cracks was just phenominal. We tried to stop at every site but the rain did hold us back. There was a particular stop that the guides specifically told you not to stop in because the air quality was so poor. Crazy, huh? So, we were in our own car and on our own schedule which I would recommend for those who are impatient. It isn't to say that a tour might be more informative, I just didn't want to go terribly slow which usually happens. We drove the entire area. My favorite part was while we drove out to the shore. The scenery was breath taking. The raining also stopped which made the experience even more enjoyable. We never saw the actual flow of lava although I read that they opened a specific area where you could a few weeks after we left. You could, in fact, see steam rising in the distance. There are little signs displayed on the lava to help guide you around. We played it safe and stayed close to the general area but you can go pretty far. I would HIGHLY recommend this experience. It was amazing!!
However, you have to take a day for the Hawaii Vulcanoes Natinal Park! My first impression wasn't great cause you still see cold lava! Take a Map and time it will be more interested so deeper you are in the Park. Don't forget to visit the vulcano beach!
Hawaii is home to the world's most massive volcano, Mauna Loa, and most active volcano, Kilauea. At the Volcanoes NP, you can get up close and personal with the landscape created by the earth's primal force and, if you're lucky, you can even witness it in action. If you're looking for an explosive eruption like Mount St Helens, you'll be disappointed. Here most likely you'll see slow-moving lava flow more reminiscent of mudslides.
You can walk on the jagged rim of a crater, gingerly pick your steps on the gnarled surface of a lava field, drive along the Crater Drive for a look at the rugged coast shaped by lava flow, or explore a lava tube the size of a subway tunnel.
A Volcano tour is a must do, if you are visiting Kona. This place is full of amazing sights, and awesome scenery. Truely a great experience.